Construction materials group SigmaRoc said it had acquired a 40% stake in Welsh quarrying group GDH for £4.9m.
The company had also negotiated an exclusive right to purchase the remaining 60% for £7.5m, on or before 31 August 2020.
The initial consideration had been funded through cash resources and credit facilities.
SigmaRoc said it planned to fund the additional consideration on the same basis, implying no dilution for equity holders.
Its net debt to Ebitda ratio would remain close to the current level of two-to-one, it added.
'GDH is a great business with a substantial asset footprint spanning across South Wales,' executive chairman David Barrett said.